1. Field of the Invention
The present invention relates to testing apparatus and method for determining physical characteristics, for instance, mechanical characteristics such as a static deflection, a dynamic axial runout, an acceleration of axial runout, a dynamic radial runout, an acceleration of radial runout, an axial tilt angle, a circularity and the like, of an optical information memory medium such as an optical disk or the like, using a laser light beam in an optical and noncontact operation.
2. Description of the Prior Art
Recently, an optical data storage medium such as an optical disk or the like has been widely used in a picture information memory searching apparatus, a picture reproducing apparatus or a music or sound reproducing apparatus. As disclosed in the report of "Optical Disk Test System" in the Yokogawa Technical Report, Vol. 31, No. 1, 1987, when the optical disk is manufactured, its various qualities is checked at an end step in a manufacturing process whether it can meet standard requirements or not. In a conventional method, the qualities of the optical disk are examined using an optical head, and focus and tracking servo voltages of the optical head are picked up. Then, the variation amounts of the optical head in focusing and tracking directions are calculated from the detected servo voltages to inspect mechanical characteristics such as a static deflection, a dynamic axial runout, an acceleration of axial runout, a dynamic radial runout, an acceleration of radial runout, an axial tilt angle, a circularity and the like of the optical disk.
In a conventional optical data storage medium testing apparatus, when the optical information is written in or read out of the optical disk in the optical and noncontact operation using the laser light beam, usually, it is necessary to move the optical head in a proper amount for correcting the deflection and the axial runout of the optical disk as its allowable errors, thereby accurately focusing the laser light beam onto the desired position of the optical disk.
That is, in this case, a focusing servo controller for maintaining a distance between an object lens of an optical head and a focusing surface of an optical disk to a constant and a tracking servo controller for tracing a track of the optical disk by moving the object lens in a radial direction for correcting a radial runout of a track of the optical disk are operated. Further, the focusing and tracking servo controllers include respective focusing and tracking coils, and the object lens attached to the optical head is controlled suitably to be moved in focusing and tracking directions by supplying electric current to the focusing and tracking coils. The current amounts to be fed to the focusing and tracking coils are proportional to the extent of movement of the object lens in the focusing and tracking directions, and, in turn, by detecting these current amounts as the voltage amounts, the variation amounts of the optical head in the focusing and tracking directions can be calculated. Then, the mechanical characteristics of the optical disk can be obtained from the variation amounts of the optical head. However, in the conventional apparatus, since the variation amounts of the optical head is calculated from the control current amounts for the focusing and tracking servo controllers, an accuracy, a resolving power and a responsive speed are low or insufficient in measuring the mechanical characteristics of the optical disk.